A Long Term Evolution (LTE) system supports two working modes, i.e., Time Division Duplex (TDD) and Frequency Division Duplex (FDD). As shown in FIG. 1, a frame structure of a TDD system is shown. Each wireless frame is 10 ms in length and is bisected into two half-frames each 5 ms in length. Each half-frame contains 8 time slots each 0.5 ms in length and 3 special fields, i.e., a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS). The sum of the length of the 3 special fields is 1 ms. Each subframe is formed of two continuous time slots, that is, the kth subframe contains a time slot 2k and a time slot 2k+1. The TDD system supports 7 uplink/downlink configurations, as shown in Table 1. Here, D is a downlink subframe, U is an uplink subframe, and S is a special subframe containing the above 3 special fields.
TABLE 1Uplink/downlink configurations of LTE TDDConfig-Cycle ofurationconversionSub frame No.No.points01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD610 msDSUUUDSUUD
for TDD, a physical Downlink Control Channel (PDCCH) schedules a Physical Downlink Shared Channel (PDSCH) within a current subframe. Furthermore, in one uplink subframe n, the HARQ-ACK information of PDSCHs in 0, 1 or more downlink subframes or HARQ-ACK information corresponding to PDCCHs indicating downlink Semi-Persistent Scheduling release (SPS release) may be fed back. The indexes of these downlink subframes are n-k, where k belongs to a set K, and the set K is determined by the TDD uplink/downlink configuration and an uplink subframe n, as shown in Table 2. For FDD, the HARQ-ACK information of PDSCHs of subframes n-k or of PDCCHs indicating SPS release is sent in the subframe n, where k=4.
TABLE 2Index set KUplink/downlinkconfig-Sub frame index nuration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7,——4, 63——7, 6, 116, 55, 4—————4——12, 8, 7,6,——————115,4, 75——13, 12, 9,———————8, 7, 5, 4,11, 66——775——77—
According to the above HARQ timing relation, in Release 8/9/10 of the LTE TDD, the maximum number of downlink HARQ processes corresponding to the above 7 TDD uplink/downlink configurations is different. Here, in order to ensure that a base station may clearly identify the respective parallel HARQ processes by HARQ process indexes in a PDCCH, the maximum number of downlink HARQ processes of each TDD uplink/downlink configuration is specified. A correspondence between the TDD uplink/downlink configuration and the maximum number of downlink HARQ processes is shown in Table 3. For FDD, the maximum number of downlink HARQ processes is 8.
TABLE 3Correspondence between the TDD uplink/downlink configurationand the maximum number of downlink HARQ processesUplink/downlinkThe maximum number ofconfigurationdownlink HARQ processes04172103941251566
The HARQ timing relation in Release 10 of the LET TDD has been described as above. Another problem related to HARQ is how to perform soft buffer processing.
In fact, there are many classes of UE according to the processing capability. The basis of classification is whether UE supports MIMO, the supported maximum number of data streams in MIMO, the size of a soft buffer and the like. Here, the soft buffer is used for storing the received soft bits when UE fails to correctly decode data sent by a base station. The soft bits in the soft buffer may be softly merged during HARQ re-transmission, so that the link performance is improved. The soft buffer processing will influence the rate matching (RM) of downlink data. In Release 10 of the LET TDD, the size of a soft buffer for the UE is described as Nsoft, and the specific value of Nsoft is related to the capability of the UE. Whether the UE is in a single-carrier mode or in a CA mode, for each code block of one transport block, rate matching is
            N      cb        =          min      (                        ⌊                                    N              IR                        C                    ⌋                ,                  K          w                    )        ,where:
            N      IR        =          ⌊                        N          soft                                      K            C                    ·                      K            MIMO                    ·                      min            ⁡                          (                                                M                  DL_HARQ                                ,                                  M                  limit                                            )                                          ⌋        ;
C is the total number of code blocks divided from a transport block;
KMIMO depends on the transmission mode of the UE; for an MIMO transmission mode, KMIMO=2, while for a non-MIMO transmission mode, KMIMO=1;
MDL_HARQ is the maximum number of downlink HARQ processes determined according to Table 3;
Mlimit is a constant 8;
Kw is the total number of code bits output by turbo coding; and
the determination method of Kc is as follows: if Nsoft=35982720, Kc=5; if Nsoft =3654144 and when UE cannot support more than two layers of spatial multiplexing when being in a downlink, KC=2; and, in other cases, KC=1.
In other words, no matter which carriers the UE works in, rate matching is performed according to the condition that the UE only configures the current one carrier. Thus, when the UE configures a plurality of cells, the processing result is that the hypothetical HARQ soft buffer for one code block in rate matching may be greater than the soft buffer capacity that the UE can support.
In Release 10 of LTE TDD, it is assumed that the UE equally divides its soft buffer to a plurality of cells. In order to better support HARQ Incremental Redundancy (IR), the base station needs to know which soft bits the UE stores when the UE fails to correctly decode one code block. Therefore, the number of the carriers configured by the UE is described as Ncells DL, and for each cell and at least KMIMO·min(MDL_HARQ, Mlimit) transport blocks, when one code block of one transport block fails to be decoded, it is stipulated in the LTE-A that the UE needs to store soft bits Wk Wk+1, . . . , Wmode(k+nSB−1,Ncb) at least for this code block, where:
            n      SB        =          min      (                        N          cb                ,                  ⌊                                    N              soft                                      C              ·                              N                cells                DL                            ·                              K                MIMO                            ·                              min                ⁡                                  (                                                            M                      DL_HARQ                                        ,                                          M                      limit                                                        )                                                              ⌋                    )        ;
is one soft bit received by the UE, and k is the smallest index among indexes of the soft bits received by the UE.
In a present LET system, if UE is in connection with a cellular network, the UE needs to receive PDSCH data sent by a base station and also D2D (Device-to-Device) signals or channels.
The D2D communication under the coverage of an LTE cell occupies uplink resources, i.e., an uplink carrier of an FDD cell or an uplink subframe of a TDD cell.
The UE needs to receive PDSCH data sent by a base station and also D2D data. When the UE fails to correctly decode the PDSCH data sent by the base station, the received soft bits are stored, and the soft bits may be softly merged during HARQ re-transmission, so that the link performance is improved. When the UE fails to correctly decode the D2D data sent by other UE, the received soft bits are stored, and the soft bits may be softly merged between multiple times of transmission of the D2D data, so that the D2D link performance is improved. At present, the soft buffer for the UE is used for storing soft bits of PDSCH data, but a soft buffer is also required to store soft bits of D2D data.
D2D includes D2D discovery and D2D communication, where D2D communication in turn includes Scheduling Assignment (SA) for scheduling D2D communication and D2D communication data. The D2D data as described in this application includes D2D discovery information, SA and D2D communication data, all of these data are transmitted for many times and many times of transmission are combined and then decoded. The number of bits of the D2D discovery information is constant, i.e., 232 bits, occupying two physical resource blocks for transmission; the number of bits of SA is related to the bandwidth of the carrier, and the number of bits of the SA is small, even smaller than that of the D2D discovery information.